Pail stacker

ABSTRACT

Pail engaging means are mounted on opposing sides of a vertical frame means which straddles a moving conveyor. A first gate means stops pail from proceeding through the vertical frame means until a stack of pails is formed and then releases the completed stack to the conveyor. A lift means enables pails engaged by the pail engaging means to be raised off the conveyor upwardly within the vertical frame means, permitting additional pails to be added to the bottom of an uncompleted stack when the pails engaged by the pail engaging means are lowered to rest on an incoming pail. A second gate means permits additional pails to pass into the vertical frame means when the conveyor pathway is not obstructed and prevents pails from passing into the vertical frame means when a pail is stopped on the conveyor by said first gate means.

United States Patent [451 May 2, 1972 Reese [54] PAIL STACKER [72] Inventor: Donald H. Reese, Orinda, Calif.

[73] Assignee: Chevron Research Company, San Francisco, Calif.

[22] Filed: Jan. 11, 1971 [21] Appl. No.: 105,200

[52] U.S. Cl ..l98/35, 209/125, 2 l4/6 BA [51 Int. Cl ..B6Sg 57/30 [58] Field of Search ..209/l22, 125; 214/6 BA; 198/35 [56] References Cited UNITED STATES PATENTS 3,037,645 6/1962 Simpkins ...2l4/6 BA 3,053,402 9/1962 Russell ..2l4/6 BA Primary Examiner-Richard A. Schacher Attorney-A. L. Snow, F. E. Johnston, R. l... Magdeburger, R. L. Freeland and N. E. Ritz [5 7] ABSTRACT Pail engaging means are mounted on opposing sides of a vertical frame means which straddles a moving conveyor. A first gate means stops pail from proceeding through the vertical frame means until a stack of pails is formed and then releases the completed stack to the conveyor. A lift means enables pails engaged by the pail engaging means to be raised off the conveyor upwardly within the vertical frame means, permitting additional pails to be added to the bottom of an uncompleted stack when the pails engaged by the pail engaging means are lowered to rest on an incoming pail. A second gate means permits additional pails to pass into the vertical frame means when the conveyor pathway is not obstructed and prevents pails from passing into the vertical frame means when a pail is stopped on the conveyor by said first gate means.

13 Claims, 7 Drawing Figures PATENTEBMAY 2|972 3.659695 SHEET 36F a 25 2a 26 27 lNVENTO-R' DONALD H. REESE PATENTED MAY 2 I972 3. 6 59 6 9 5 SHEET u 0F 4 INVENTOR I 8 DONALD H. REESE PAIL STACKER FIELD OF THE INVENTION This invention relates to a device for stacking pails and, more particularly, relates to a device for stacking pails as they move along a continuous moving conveyor.

BACKGROUND OF THE INVENTION The art of stacking objects which are being transported on a continuous moving conveyor has developed primarily in the area of elevator means which raise each object, usually boxes or other rectangularly shaped objects, individually from the moving conveyor belt and then set the objects down on top of each other. U.S. Pat. No. 2,948,382, issued to Russell, disclose a vertical stack pathway within which an elevator means raises objects in spaced relation. When a predetermined number of objects have been raised above the moving conveyor belt, the direction of the elevator is reversed and the boxes are set down on top of each other. U.S. Pat. No. 2,897,949, issued to l-Iuisking, discloses an elevator which lifts boxes individually from one moving conveyor belt and, when a predetermined number of boxes have been raised, allows all boxes to drop onto another moving conveyor belt. U.S. Pat. No. 2,919,821, issued to Young, discloses a continuous elevator means which raises boxes from a moving conveyor belt and sets them down in a stack on a platform positioned above the moving conveyor belt. U.S. Pat. No. 3,288,269, issued to Roth et al.; discloses a system of dual conveyor belts whereby objects on one conveyor belt are allowed to drop onto objects on the other conveyor belt causing stacks to be formed thereby. By and large, the art has consisted of complex mechanical devices for maneuvering moving objects into vertically stacked relation The stacking of objects such as boxes and cylindrical pails is essential to the efficient operation of manufacturing and packaging plants. Individual boxes or cylindrical pails must be stacked in order to insure efficient transportation or storage. The costs of labor are prohibitive to the extent that automatic stacking devices are highly desirable. Although automatic stacking devices are desirable, it is preferable that they be of simple design and moderate cost. Simplicity in design lessens the likelihood of mechanical breakdown and decreases the costliness of repair in the event of mechanical breakdown. Simplicity of design, generally, also renders the device easier to operate so that highly trained mechanics are not required to oversee their operation. A great difficulty with existing devices is that they were complex mechanical machines which were costly to construct, and difficult to operate and repair. Many of the stacking devices were constructed with gears and moving chain belts which created a hazard to workers in the vicinity. A further disadvantage of existing stacking devices is that they would not allow odd size objects to pass through when the stacking device is not in operation.

A particular problem encountered in stacking pails is the need to compensate for the bail or handle which is typically attached to opposite sides of the pail. If the pail is maneuvered into a vertical stack by a means which engages it, the engaging means must avoid the bail so that the pail can be engaged firmly and so that the bail is not bent or detached from the pail. Most existing mechanical stacking means are not able to avoid bails. Others would be able to avoid them only if the pails were rotated into a particular orientation before stacking, thus necessitating additional equipment and processing.

An additional problem encountered in stacking pails is that of forming even and stable stacks so that the stacks may be returned to a moving conveyor and will remain on the conveyor without toppling over. Often, the bottom ends of pails are smaller than the upper ends, making it possible to stack the pails off center. In order to avoid uneven stacking, it is necessary to grip the pails firmly, lift them in a substantially vertical line and release the pails cleanly so they are not jostled out of alignment with the other pails when the pail engaging means disengages. Available mechanical stacking means are not capable of consistently producing. even and stable stacks of pails.

It is an object of this invention, then, to stack pails with a pail stacker which does not interfere with and is not impeded by the bails on the pails being stacked.

It is also an object of this invention to stack pails with a pail stacker which does not damage the balls of the pails being stacked.

It is also an object of this invention to stack pails evenly in stable stacks by engaging the pails firmly and releasing them cleanly in vertical alignment with other pails.

It is a further object of this invention to provide a simply constructed pail stacking device which is safe to operate and inexpensive to construct.

It is an additional object of this invention to provide a pail stacking device which does not inhibit the steady flow of pails on a moving conveyor.

It is a final object of this invention to provide a pail stacker which can quickly and effectively be cleared so that odd-size pails or barrels may pass through the stacker without being stacked.

SUMMARY OF THE INVENTION The pail stacker of my invention forms stable stacks of pails by lifting pails above the moving conveyor and depositing them on top of incoming pails. A pair of platen means is machined to fit the upper lip of the pails being stacked. The platen means is designed to fit around the bail and other irregularities on the exterior of the pails. These platen means grip a single pail and a lift means lifts the platen means with the engaged pail above the moving conveyor. When an additional pail has been introduced to the pail stacking column, the engaged pail is deposited on it. The platen means cleanly disengages from the engaged pail and moves down to the bottom pail. The platen means then grips the upper lip of the bottom pail of the partially completed stack and the lift means lifts both pails above the moving conveyor and deposits them on an additional incoming pail. The operation of the platen means and the lift means is controlled by a network of light sources, photoeyes, reflectors, a pair of stop means which stops pails in alignment with the stack being formed and another pair of stop means which allows additional pails to be introduced to the pail stacking column at the appropriate moment. The platen means and the lift means may be hydraulically or pneumatically operated or, in the least preferred em bodiment, mechanically operated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an end view of the pail stacker of my invention illustrating the way in which the platen means engages the upper lip ofa pail. The phantom portion of the drawing illustrates the position to which the lift means raises the platen means and the engaged pail above the moving conveyor.

FIG. 2 is a side view of the pail stacker of my invention illustrating the way in which pails are prevented from entering the pail stacking column by a pair of front stop means while a pail rests on the moving conveyor in the pail stacking column.

FIG. 3 is a plan view of the pail stacker, illustrating the support assembly on which platen means are mounted to insure stable lifting.

FIG. 4 is a schematic diagram showing the photoeyes and reflectors which control the operation of the platen means, the lift means, and the pairs of stop means. Phantom pail positions are included to facilitate understanding of the locations at which individual photoeye lines of sight are intercepted.

FIG. 5 is a detailed side view ofa single platen means in engagement with a phantom pail.

FIG. 5A is a detailed side view of the platen means immediately after it has become disengaged from a pail.

FIG. 6 is a detailed plan view ofa single platen means in engagement with a phantom pail.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, it can be seen that vertical frame means 20 defines a column for the stacking of pails. Pail 7 has been introduced to the pail stacking column by means of rollers 21 mounted on girders 31. Pail 7 is prevented from passing through the pail stacking column by back stop means 24 which contact the pail along the forward side. Pail 7 is centered within the column by the action of moving rollers 21 which attempt to move pail 7 in the direction of their rotation and thereby force pail 7 firmly against back stops 24. Pail 7 has been channeled to the center of the moving conveyor by means of guide rails 45.

When pail 7 is firmly in place in the center of the pail stacking column defined by vertical frame means 20, platen means 12 and 13 are moved into engagement with the upper lip of Pail 7. Platen means 12 and 13 are moved into engagement with pail 7 by means of plungers 16 and 17 driven by pneumatic or hydraulic cylinders 10 and 11, respectively. Hydraulic or pneumatic cylinders 10 and 11 are capable of slight rotation about their junction with support assembly 66. It is evident that platen means 12 and 13 have been carefully machined to avoid interfering with bail 8 and bail support 22. Platen means 12 and 13 fit snugly underneath lid 9, as shown in FIGS. 1, 2 and 3.

When platen means 12 and 13 are firmly engaged on the upper lip of pail 7, arms 15 and 14, respectively, trip limit switches 18 and 19, respectively, so that pneumatic or hydraulic cylinder 34 is activated. When cylinder 34 is activated, plunger 35 is drawn up raising support assembly 66 from lower position 30 to raised position 30.

When support assembly 66 is raised about halfway, the bottom of pail 7 will clear light beam E-B for photoeye 58, shown in FIG. 4, and the pneumatic or hydraulic pressure within cylinders 10 and 11 is released. Pail 7 remains in place between platen means 12 and 13 by the action of its weight. Cylinders 10 and 11 are spring loaded but the spring tension is carefully adjusted so that platen means 12 and 13 will rotate out of alignment with the pail stacking column only when the engaged pail is set down on an incoming pail, or conveyor.

FIG. 2 illustrates the usefulness of front stops 40. While pail 7 remains on the conveyor within the pail stacking column, front stops 40 remain raised. Additional pail 6 will be allowed into the pail stacking column only when pail 7 is raised within the column, clearing light beam D-B for photoeye 56, shown in FIG. 4. Front stops 40 and back stops 24 are moved by electropneumatic or electrohydraulic means 42 and 41, respectively. It is clear that guide rails 45 channel incoming pails into alignment with the center of the moving conveyor.

From FIG. 2 it can be seen that support assembly 66 moves smoothly in an up and down motion by means of outer cylinder 26 and inner shaft 25. In the lower position, arm 4 which is mounted on cylinder 26 trips limit switch 3 and thereby activates the platen means to engage the pail on the moving conveyor when light beam E8 to photoeye 58 is blocked, as shown in FIG. 4. Arm 28, also mounted on cylinder 26 trips limit switch 27 when support assembly 66 is in the raised position. The tripping of limit switch 27 permits cylinder 34 to lower plunger 35 when light beam E-B for photoeye 58 is again blocked by a pail. The exact level reached by support assembly 66 is determined by the adjustment 37 on the upper end of plunger 33. Pneumatic or hydraulic cylinder 32 and plunger 33 is mounted in line with pneumatic or hydraulic cylinder 34 and plunger 35. As stated previously, cylinder 34 is used to lift support assembly 66 to accomplish the stacking of pails. Cylinder 32 is activated separately by an external switch and is used in conjunction with cylinder 34 to raise support assembly 66 high above the moving conveyor to permit odd size pails or barrels to pass through vertical frame means without being stacked or impeded by the presence of the stacking device. When cylinders 32 and 34 are activated together, the stacking device is rendered inoperable.

FIG. 3 illustrates the relationship between platen means 12 and 13 and support assembly 66. Stable lifting is insured because platen means 12 and 13 remain on the same horizontal level. Support assembly 66 is guided vertically by means of cylinder 26 mounted on inner shaft 25 and wheels 29 which ride on vertical lip 36. Pails 5 are shown to be in physical contact with pail 6 which rests against front stops 40, although, in actual practice, pails reach front stops 40 in an intermittent fashion.

Referring now to FIG. 4, the automatic operation of my pail stacker can be visualized by observing the series of phantom pail positions 50, 51 and 52 which represent positions occupied by individual pails that are fed into the pail stacking column and by observing phantom pail positions 52, 53 and 54 which represent positions occupied by completed stacks of pails which are released from the column. When the power is turned on, back stops 24 are in a raised position and front stops 40 are in a lowered position so that a pail at position 50 would not be stopped. The pail would pass underneath photoeye line of sight A-C since it elevated above the height of the pails being stacked. The pail then passes through photoeye line of sight D-B. When photoelectric line of sight D-B is intercepted, the light beam to photoeye 56 is cut off and front stops 40 are raised. The pail next occupies position 52 and thereby intercepts photoeye line of sight E-B thereby cutting off the light beam to photoeye 58. At position 52 photoeye line of sight D-B remains intercepted so that front stops 40 remain raised to prevent an additional pail from proceeding along the conveyor belt and colliding with the pail at position 52.

The switch associated with photoeye 58 and reflector 61 is triggered when photoelectric line of sight E-B is intercepted and lowers support assembly 66 so that platen means 12 and 13 are in a position opposite the upper lip of the pail occupying position 52. The height of the support assembly is suffcient to allow platen means 12 and 13 to clear the bail of the pail occupying position 52. Then, as limit switch 3 is tripped by arm 4, platen means 12 and 13 moves in to engage the pail as shown, for example, in FIG. 3. As described infra, the platen means has been carefully adjusted to fit underneath the lip formed by the lid of the pail. When the platen means has securely engaged the pail occupying position 52, limit switches 18 and 19 are tripped by arms 15 and 14, respectively, to activate pneumatic or hydraulic cylinder 34 to lift the support assembly with platen means and the engaged pail above the conveyor belt within the pail stacking column in order to permit the entry of an additional pail. Front stops 40 are lowered as soon as the pail being raised clears photoeye line of sight D-B thereby restoring the light signal received by photoeye 56.

The additional pail rides along the moving conveyor, enters the pail stacking column, rests against back stops 24 and undergoes the process described above with the result that the first pail is placed on top of the additional pail. The springloaded feature of the platen means permits platen means 12 and 13 to break cleanly away from the first pail as soon as its weight rests on the incoming pail. Lift means 34 then lowers support assembly 66 to a height opposite and slightly below the upper lip of the incoming pail.

When the incoming additional pail is securely engaged in a manner to avoid interfering with or damaging the bail, limit switches 18 and 19 are again triggered by arms 15 and 14, respectively, to activate pneumatic or hydraulic cylinder 34 to lift support assembly 66 with platen means 12 and 13 and the engaged pail with the stacked pail on top within the stacking column to allow a third pail to be introduced. Front stops 40 are again lowered as soon as photoeye line of sight DH is cleared. In the embodiment shown in FIG. 5, photoeye line of sight A-C will be intercepted at this point by the pail which rests on top of the pail engaged by platen means 12 and 13. The switch associated with photoeye 55 and reflectors 62 and 64 lowers back stops 24 once the two pails are lowered onto the third incoming pail provided photoeye line of sights 1-1-0 and K-G, associated with photoeye 59 and reflectors 63 and 65, are clear downstream. Thus, photoeye line of sight A-C controls the height of the stack of stacking of as few as two placed in a stable stack.

In the embodiment illustrated photoeye 57 and reflector 60 are positioned at opposite sides of the pail stacking column and provide a safety override for the total operation of the stacking device. If photoeye line of sight I-J is not cleared every 6 seconds, the conveyor is shut down. This safety device operates on the assumption that it is highly probable that the pallatizer operation has become fouled up or the conveyor has stopped if photoelectric line of sight H is not cleared every 6 seconds. This safety device also detects the rare instances in which the stacking device malfunctions. The device prevents major breakdowns and permits an operator to respond to an audio or visual alarm whenever minor foul-ups occur.

FIG. 5 shows platen means 68 in engagement with pail 69. Edge 82 of platen means 68 fits underneath lip 88 of pail 69. Notch 83 in platen means 68 permits the platen means to avoid pail support 90. The contour of platen means 68 is also figured to avoid irregularity 89 in pail 69, an irregularity which is often introduced on pails to increase the wall strength.

Platen means 68 rotates about junction 81 with member 91 which is connected to support assembly 66 whenever plunger 71 is withdrawn into plunger 70. Plunger 71 is connected to member 78 which is in turn connected to member 77 by means of swivel junction 76. Member 77 is then connected to platen means 68. The exact position at which platen means 68 engages pail 69 is determined by the adjustment of screw 73 threaded through nut 72 and bar 86 or bar 87, as shown in FIG. 6 which are attached to platen means 68 by means of member 74. The motions of engagement and disengagement of platen means 68 are rendered smoother by the ability of pneumatic or hydraulic cylinder 70 to rotate about point of contact 84 with the support assembly 66.

Limit switch 80 is tripped by arm 86 when platen means 68 firmly engages pail 69. A fine adjustment is necessary for firm engagement and for clean disengagement. As described previously, the pneumatic or hydraulic pressure on plunger 71 is released when pail 69 reaches the midway position. It is evident that the weight of pail 69 on platen means 68 will hold the pail in place on the platen means. Hydraulic or pneumatic cylinder 70 is spring loaded so that when support assembly 66 is lowered to the point at which pail 69 rests on top of an additional incoming pail and the weight on platen means 68 is released, plunger 71 is pulled into pneumatic or hydraulic cylinder 70 with the result that platen means 68 is rotated into an upright position to permit maximum clearance for the pails.

The upright position or disengaged position of platen means 68 is illustrated in FIG. 5A. As shown, support assembly 66 is slightly lower than in FIG. 5. This is due to the fact that platen means 68 must be moved slightly below lip 88 on pail 69 so that the rotation about junction 81 can clear lip 88. FIG. 5A clearly shows the open position of contact 79 on limit switch 80. In the disengaged position, platen means 68 and vertical support member 91 clear bail 8 as well as ball support 90.

At no time during the engagement or disengagement of the pails does platen means 68 come in contact with bail 8 or bail support 90 so that no bail or bail support damage occurs. The close engagement of platen means 68 with pail 69 is illustrated in FIG. 6. The leading edge of platen means 68 is curved to conform with the exterior curvature of pail 69. The phantom line 88 illustrates how the upper lip of pail 69 extends over the leading edge 82 of platen means 68. It is also clear that a dual adjustment ofthe engagement of platen means 68 with pail 69 is possible by means of screws 73 on threaded arms 86 and bars 91.

While a specific embodiment of my invention has been described in detail, the scope of my invention is intended to be limited only by the scope and spirit ofthe appended claims.

lclaim:

1. A pail stacker for stacking pails without orienting the balls thereon and without damaging the bails during stacking comprising vertical frame means defining a column for the pails. It can permit the pails or as many pails as can be stacking of pails, conveyor means passing through said vertical frame means, said conveyor means forming an in-feed means to deliver pails to said column and an out-feed means to remove stacks with a predetermined number of pails from said column, first gate means to stop pails in the in-feed path of said column in alignment with said column after delivery thereto by said in-feed means and to release said stacks when they contain said predetermined number of pails to said outfeed means, pail engaging means affixed to saidvertical frame means which engage pails without hitting the bails thereof, lift means to vary the vertical position of said pail engaging means between the lower position which the pail engaged by said pail engaging means occupies in said column immediately after delivery by said in-feed means and a higher position in said column which permits delivery by said in-feed means of an additional pail to said column, said lift means being cooperatively associated with said pail engaging means to place previously engaged and lifted pails on top of the pail newly delivered to said column by said in-feed means, and second gate means to prevent delivery by said in-feed means ofa pail to said column while a pail occupies said lower position and to permit delivery by said in-feed means of a pail to said column when no pail occupies said lower position of said column.

2. The pail stacker of claim 1 in which said pail engaging means comprises a single platen means mounted on one side of said vertical frame means and a fixed pail engaging jaw mounted on the opposite side of said vertical frame means.

3. The pail stacker of claim 1 in which said pail engaging means comprises a pair of platen means mounted on opposite sides of said vertical frame means.

4. The pail stacker of claim 3 in which said lift means and said pail engaging means are hydraulically operated.

5. The pail stacker of claim 3 in which said lift means and said pail engaging means are pneumatically operated.

6. The pail stacker of claim 5 in combination with a means to raise said platen means and lift means above said conveyor means to permit odd size pails or barrels to pass through said vertical frame means without being stacked.

7. A pail stacker for stacking pails without orienting the balls thereon and without damaging the bails during stacking comprising vertical frame means defining a column for the stacking of pails, conveyor means passing through said vertical frame means, said conveyor means forming an in-feed means to deliver pails to said column and an out-feed means to remove stacks with predetermined numbers of pails from said column, pail engaging means affixed to said vertical frame means which engage pails without hitting the bails thereof, a first light source mounted transverse to said conveyor means and across said column and a first light sensitive detector mounted opposite to said first light source, a first light path from said first light source to said first detector being blocked when a pail has been delivered to said column by said in-feed means, said detector being cooperatively associated with said pail engaging means and a lift means to cause said pail engaging means to engage the pail blocking said first light path and to cause said lift means to lift the pail engaging means with engaged pail from the lower position which The pail engaged by said pail engaging means occupies in sald column immediately after delivery by said in-feed means to a higher position in said column which permits delivery by said in-feed means of an additional pail to said column, said first detector also being cooperatively associated with a first stop means to stop pails delivered by said in-feed means in alignment with said column when said first light path is blocked, a second light source mounted transverse to said conveyor means and across said column and a second light sensitive detector mounted opposite to said second light source, a second light path from said second light source to said second detector being blockedwhenever a pail or any part thereof would prevent the delivery of an additional pail to said column by said in-feed means, said second detector being cooperatively associated with a second stop means to stop pails from being delivered to said column when said second light path is blocked and to permit an additional pail to be delivered to said column by said in-feed means when said second light path is clear, and a third light source mounted transverse to said conveyor means and across said column and a third light sensitive detector mounted opposite to said third light source, the light path from said third source to said third detector being blocked when said lift means raises said pail engaging means with engaged pails to permit the final additional pail to be added to the bottom of a partially completed stack to reach said predetermined number, said third detector overriding said second detector to raise said second stop means and overriding said first detector to lower said first stop means, said override of said first and second detectors terminating when said stack with said predetermined number of pails has been removed from said column by said out-feed means.

8. The pail stacker of claim 7 in which said pail engaging means comprises a single platen means mounted on one side of said vertical frame means and a fixed pail engaging jaw mounted on the opposite side of said vertical frame means.

9. The pail stacker of claim 7 in which said pail engaging means comprises a pair of platen means mounted on opposite sides of said vertical frame means, said platen means being spring loaded so that they cleanly disengage from an engaged pail when said engaged pail is lowered onto an additional pail.

10. The pail stacker of claim 9 in which said lift means and said pail engaging means are hydraulically operated.

11. The pail stacker of claim 9 in which said lift means and said pail engaging means are pneumatically operated.

12. The pail stacker of claim ll in combination with a means to raise said platen means and lift means above said conveyor means to permit odd size pails or barrels to pass through said vertical frame means without being stacked.

13. The pail stacker of claim 12 in combination with a fourth light source mounted transverse to said conveyor means and across said column and a fourth light sensitive detector mounted opposite to said fourth light source. said con veyor means, platen means and lift means being de-energized if the light path between said fourth light source and said fourth detector is not cleared at least once every 6 seconds. 

1. A pail stacker for stacking pails without orienting the bails thereon and without damaging the bails during stacking comprising vertical frame means defining a column for the stacking of pails, conveyor means passing through said vertical frame means, said conveyor means forming an in-feed means to deliver pails to said column and an out-feed means to remove stacks with a predetermined number of pails from said column, first gate means to stop pails in the in-feed path of said column in alignment with said column after delivery thereto by said in-feed means and to release said stacks when they contain said predetermined number of pails to said out-feed means, pail engaging means affixed to said vertical frame means which engage pails without hitting the bails thereof, lift means to vary the vertical position of said pail engaging means between the lower position which the pail engaged by said pail engaging means occupies in said column immediately after delivery by said in-feed means and a higher position in said column which permits delivery by said in-feed means of an additional pail to said column, said lift means being cooperatively associated with said pail engaging means to place previously engaged and lifted pails on top of the pail newly delivered to said column by said in-feed means, and second gate means to prevent delivery by said in-feed means of a pail to said column while a pail occupies said lower position and to permit delivery by said in-feed means of a pail to said column when no pail occupies said lower position of said column.
 2. The pail stacker of claim 1 in which said pail engaging means comprises a single platen means mounted on one side of said vertical frame means and a fixed pail engaging jaw mounted on the opposite side of said vertical frame means.
 3. The pail stacker of claim 1 in which said pail engaging means comprises a pair of platen means mounted on opposite sides of said vertical frame means.
 4. The pail stacker of claim 3 in which said lift means and said pail engaging means are hydraulically operated.
 5. The pail stacker of claim 3 in which said lift means and said pail engaging means are pneumatically operated.
 6. The pail stacker of claim 5 in combination with a means to raise said platen means and lift means above said conveyor means to permit odd size pails or barrels to pass through said vertical frame means without being stacked.
 7. A pail stacker for stacking pails without orienting the bails thereon and without damaging the bails during stacking comprising vertical frame means defining a column for the stacking of pails, conveyor means passing through said vertical frame means, said conveyor means forming an in-feed means to deliver pails to said column and an out-feed means to remove stacks with predetermined numbers of pails from said column, pail engaging means affixed to said vertical frame means which engage pails without hitting the bails thereof, a first light source mounted transverse to said conveyor means and across said column and a first light sensitive detector mounted opposite to said first light source, a first light path from said first light source to said first detector being blocked when a pail has been delivered to said column by said in-feed means, said detector being cooperatively associated with said pail engaging means and a lift means to cause said pail engaging means to engage the pail blocking said first light path and to cause said lift means to lift the pail engaging means with engaged pail from the lower position which The pail engaged by said pail engaging means occupies in saId column immediately after delivery by said in-feed means to a higher position in said column which permits delivery by said in-feed means of an additional pail to said column, said first detector also being cooperatively associated with a first stop means to stop pails delivered by said in-feed means in alignment with said column when said first light path is blocked, a second light source mounted transverse to said conveyor means and across said column and a second light sensitive detector mounted opposite to said second light source, a second light path from said second light source to said second detector being blocked whenever a pail or any part thereof would prevent the delivery of an additional pail to said column by said in-feed means, said second detector being cooperatively associated with a second stop means to stop pails from being delivered to said column when said second light path is blocked and to permit an additional pail to be delivered to said column by said in-feed means when said second light path is clear, and a third light source mounted transverse to said conveyor means and across said column and a third light sensitive detector mounted opposite to said third light source, the light path from said third source to said third detector being blocked when said lift means raises said pail engaging means with engaged pails to permit the final additional pail to be added to the bottom of a partially completed stack to reach said predetermined number, said third detector overriding said second detector to raise said second stop means and overriding said first detector to lower said first stop means, said override of said first and second detectors terminating when said stack with said predetermined number of pails has been removed from said column by said out-feed means.
 8. The pail stacker of claim 7 in which said pail engaging means comprises a single platen means mounted on one side of said vertical frame means and a fixed pail engaging jaw mounted on the opposite side of said vertical frame means.
 9. The pail stacker of claim 7 in which said pail engaging means comprises a pair of platen means mounted on opposite sides of said vertical frame means, said platen means being spring loaded so that they cleanly disengage from an engaged pail when said engaged pail is lowered onto an additional pail.
 10. The pail stacKer of claim 9 in which said lift means and said pail engaging means are hydraulically operated.
 11. The pail stacker of claim 9 in which said lift means and said pail engaging means are pneumatically operated.
 12. The pail stacker of claim 11 in combination with a means to raise said platen means and lift means above said conveyor means to permit odd size pails or barrels to pass through said vertical frame means without being stacked.
 13. The pail stacker of claim 12 in combination with a fourth light source mounted transverse to said conveyor means and across said column and a fourth light sensitive detector mounted opposite to said fourth light source, said conveyor means, platen means and lift means being de-energized if the light path between said fourth light source and said fourth detector is not cleared at least once every 6 seconds. 